Power supply device for low-voltage electronic residual current circuit breakers

ABSTRACT

A power supply device for low-voltage electronic residual current circuit breakers, comprising:  
     an electronic rectifier stage, suitable to receive in input a mains voltage and to generate a first unipolar voltage whose value depends on the value of the mains voltage; and  
     an electronic adjustment stage, suitable to receive in input the first unipolar voltage and a current and to generate in output a second unipolar voltage of adjustable value.  
     Its particularity consists of the fact that the electronic adjustment stage comprises first electronic means suitable to perform an active adjustment of the current in input to the electronic adjustment stage, so as to keep the second unipolar voltage at a predefined constant value.

DESCRIPTION

[0001] The present invention relates to a power supply device forlow-voltage electronic residual current circuit breakers (RCCBs) and thelike.

[0002] In particular, the power supply device, according to the presentinvention, is suitable for use in electronic RCCBs for applications ofthe single-phase or multiple-phase (two-phase, three-phase, et cetera)with operating voltages around 1000 V or less.

[0003] Many examples of low-voltage electronic RCCBs are known in thebackground art.

[0004] The structure of a low-voltage electronic RCCB of the known typeis illustrated schematically with reference to FIG. 1.

[0005] In general, a low-voltage electronic RCCB, designated by thereference numeral 1, comprises a sensor 2, which is suitable to generatea signal 3, indicative of the presence of an imbalance current due to aground-fault, in an electrical network 4 of the single- or multi-phasetype.

[0006] The signal 3 is received in input by an electronic protectionsystem 5, which generates control signals 6 in order to drive, forexample, an electromagnetic release device and/or electronic signalingdevices or auxiliary electronic devices (reference 8), aimed atproviding signals related to the status of the apparatus or circuitbreaker.

[0007] The electronic protection system 5, the electromagnetic release 7and the signaling devices 8 must, for their correct operation, besupplied with a given electrical power level P_(AL), generally providedby an electronic power supply device 9, which has in output a powersupply voltage V_(AL).

[0008] Traditionally, the electronic power supply device 9 can berealized according to different approaches.

[0009] According to a first constructive approach, the electronic powersupply device 9 is structured, so as to receive electrical power (dashedarrow 10) directly from the sensor 2, which is used to detect the vectorimbalance of the currents, between the phases of the electrical network4. This type of approach, which offers the unquestionable advantage ofensuring power supply (and consequently operation of the RCCB) in amanner virtually independent of the mains voltage, has considerabledrawbacks. In fact, the electrical power P_(AL) that can be madeavailable by the power supply device 9 is generally reduced (a fewhundred mVA) and allows to supply an electronic protection system 5 oran electromagnetic release 7, which have to be necessarily of thelow-power type. It also becomes difficult to supply power to otherdevices, which are accessories or are of the auxiliary type. Thus, onecan say that the power supply devices 9, provided according to the firsttype of approach described, are often affected by considerable operatinglimitations.

[0010] In an alternative constructive approach, the electronic powersupply device 9 is structured so as to obtain electric power (dashedarrow 11) directly from the electrical network 4. In order to be able tosupply the electric power P_(AL), voltages and currents (V_(IN) andI_(IN)) of the phases of the electric network 4 are made available bymeans of a rectifier bridge and an appropriate network of resistive andcapacitive passive elements (not shown). A network of passive elementsof the nonlinear type 12 is generally used in order to widen theavailable range of the input supply voltage.

[0011] Practice has shown that also this constructive approach hasconsiderable drawbacks, even though it is inherently very robust andcapable of costantly supplying an adequate power level P_(AL).

[0012] The use of a network of passive elements makes it difficult toensure that a stable power supply condition is reached with a lowtransient period, when supply voltage ranges very different from eachother have to be adopted.

[0013] Furthermore, in this case, it is necessary to dissipate as heatthe excess available energy for the higher supply voltage ranges.

[0014] Moreover, the use of nonlinear passive components is very oftencritical, since these components generally have relatively large sizeand considerably high costs, in comparison with the costs of commonlyused active or passive circuit elements.

[0015] Additionally, owing to the need to optimize the working point ofthe electrical network of passive elements, according to the suppliedelectric power, it is often necessary to provide a different type ofpower supply device 9 for each different supply voltage range, which hasto be supplied.

[0016] For these reasons, the practice has shown that, often, the use ofpower supply devices of this type is scarcely flexible, leading to aconsequent increase in production costs, installation costs andoperating costs of the electronic RCCB.

[0017] The aim of the present invention is to provide a power supplydevice for low-voltage electronic RCCBs, which allows obviating thedrawbacks above described.

[0018] Within the scope of this aim, an object of the present inventionis to provide a power supply device for low-voltage electronic RCCBs,which allows using relatively high input supply voltage ranges whilemaintaining dissipated power at relatively low levels.

[0019] Another object of the present invention is to provide a powersupply device for low-voltage electronic RCCBs, which allows providingan electric power sufficient to supply even relatively high-powerelectromagnetic release devices.

[0020] Another object of the present invention is to provide a powersupply device for low-voltage electronic RCCBs, which has a reducedtransient time before achieving the steady-state condition.

[0021] Another object of the present invention is to provide a powersupply device for low-voltage electronic RCCBs, which is relativelycompact, easy to manufacture and at relatively low costs.

[0022] Thus, the present invention provides a power supply device forlow-voltage electronic RCCBs, comprising:

[0023] an electronic rectifier stage, suitable to receive in input amains voltage and to generate a first unipolar voltage, the value ofsaid first unipolar voltage depending on the value of said mainsvoltage; and

[0024] an electronic adjustment stage, suitable to receive in input,from said electronic rectifier stage, said first unipolar voltage and afirst current and to generate in output a second unipolar voltage ofadjustable value.

[0025] The power supply device, according to the present invention, ischaracterized in that said electronic adjustment stage comprises firstelectronic means, suitable to perform an active adjustment of said firstcurrent, so as to keep said second unipolar voltage at a predefinedadjustable value.

[0026] The active adjustment of said first current, in input to saidelectronic adjustment stage, allows to obtain an output voltage, whichcan be easily predefined at a chosen value, considerably increasing theoperating flexibility of the power supply device, according to theinvention. The term “active adjustment” of said first current is used todesignate a type of adjustment, which allows to vary the flow of saidfirst current, by using active semiconductor devices. In this manner,the power supply device, according to the present invention, allows toconvert a variable mains voltage into a power supply voltage, which canhave a predefined adjustable value, preferably constant.

[0027] The active adjustment of said first current furthermore allows toreduce power dissipation to negligible values, by means of choosing themost appropriate adjustment modes, such as for example a nonlinearadjustment mode of the switching type, in which the flow of said firstcurrent is varied according to an ON/OFF mode.

[0028] Further characteristics and advantages of the power supplydevice, according to the present invention, are described in greaterdetail hereinafter with particular reference to the accompanyingdrawings, wherein:

[0029]FIG. 1 is a schematic view of a low-voltage electronic RCCBs, of aknown type; and

[0030]FIG. 2 is a schematic view of a power supply device, according tothe present invention; and

[0031]FIG. 3 is a schematic view of a preferred embodiment of a powersupply device, according to the present invention; and

[0032]FIG. 4 plots schematically some currents and voltages in theembodiment of the power supply device, according to the presentinvention, shown in FIG. 3.

[0033] With reference to FIG. 2, the power supply device, according tothe present invention, generally designated by the reference numeral 20,comprises an electronic rectifier stage 21. The electronic rectifierstage 21 receives in input a mains voltage V_(NET) and generates a firstunipolar voltage V_(IN), whose value depends on the value of the mainsvoltage V_(NET). Advantageously, the electronic rectifier stage 21 maycomprise a diode bridge, connected so as to obtain a unipolar voltage,which is not necessarily constant. In fact, the first unipolar voltageV_(IN) can comprise, for example, a waveform, which varies according tothe modulus of one of the phase voltages. Obviously, depending on theavailable type of mains, the electronic rectifier stage can be adaptedto draw voltage from a single-phase or multiple-phase mains. The powersupply device 20 furthermore comprises an electronic adjustment stage24, which is suitable to receive in input the first unipolar voltageV_(IN) and a first current I_(IN). The electronic adjustment stage 24generates in output a second unipolar voltage V_(OUT), having anadjustable value (for example an adjustable instantaneous values or anadjustable average value or the like). The second output voltage V_(OUT)constitutes, in practice, the supply voltage, which is provided inoutput by the power supply device 20.

[0034] The power supply device 20 comprises first electronic means 27 inorder to perform an active adjustment of the first current I_(IN) ininput to the electronic adjustment stage 24, so as to keep the secondunipolar voltage V_(OUT) at a predefined constant value.

[0035] The first electronic means 27 perform an active adjustment of thefirst current I_(IN) in input to the electronic adjustment stage 24.This allows providing, in output from the first electronic means 27, asecond current I_(OUT), which has an adjustable average value.

[0036] Preferably, the first electronic means 27 perform an activeadjustment of the first current I_(IN), according to a nonlinearadjustment mode and particularly according to a switching-typeadjustment mode. In particular, the first current I_(IN) is preferablyvaried according to an ON/OFF mode. In this case, the second currentI_(OUT) can therefore have a pulsed-type waveform with an easilyadjustable pulse width and repetition period.

[0037] Again with reference to FIG. 2, the electronic adjustment stage24 advantageously comprises a charge accumulation circuit 23, which iselectrically connected to the first electronic means 27. The chargeaccumulation circuit 23 receives in input the second current I_(OUT) andgenerates in output the second unipolar voltage V_(OUT). Thus, the valueof the second unipolar voltage V_(OUT) is adjustable, according to theaverage value of the second current I_(OUT).

[0038] Preferably, the electronic adjustment stage 24 comprises secondelectronic means 26, which are electrically connected to the firstelectronic means 27 and generate control signals V_(COM) in order tokeep the second current I_(OUT) below a predefined maximum threshold. Inparticular, the second electronic means 26 are suitable to limit theamplitude of the pulses of the second current I_(OUT). In this manner,sudden variations of the voltage V_(IN), caused by sudden changes in themains voltage, are prevented from causing high current pulses of thecurrent I_(OUT), which may happen since the second current I_(OUT)trends intrinsically to charge, in the shortest possible time, thecharge accumulation circuit 23. This fact implies that in the powersupply device 20, the voltage V_(OUT) remains at a substantiallyconstant value despite the occurrence of sudden mains voltagevariations. This is particularly advantageous, since it prevents thepossibility of damage to the electronic components connected downstreamthe power supply device 20.

[0039] Preferably, the electronic adjustment stage 24 comprises thirdelectronic means 28, which are electrically connected to the firstelectronic means 27 and are suitable to increase the stability of theadjustment stage 24. Advantageously, the third electronic means 28 senda feedback signal V_(FREQ) to the first electronic means 27 in order toadjust the slope of the rising/falling edges related to the pulses ofthe second current I_(OUT) In this manner it is possible to reduce theonset of electromagnetic noise.

[0040] A preferred embodiment of the electronic adjustment stage 24,regarding the power supply device 20, according to the invention, is nowdescribed schematically with reference also to FIG. 3.

[0041] According to this embodiment, the first electronic means 27comprise an electronic interruption circuit 41, which is advantageouslysuitable to enable/interrupt, following the reception of anenable/disable signal V_(AB), the first current I_(IN), in input to theadjustment stage 24. Advantageously, the first electronic means 27 alsocomprise an electronic control circuit, which comprises a comparatorcircuit block 44 and an enabling circuit block 45. The comparatorcircuit block 44 is suitable to generate a control signal 47 if thevoltage V_(OUT) assumes values below or above a predefined range. Theenabling circuit block 45 is suitable to generate, following thereception of the control signal 47, an enable/disable signal V_(AB) forthe electronic interruption circuit 41.

[0042] Advantageously, the electronic interruption circuit 41 comprisesone or more active electronic semiconductor devices Q₁, such as forexample transistors of the MOSFET, BJT or IGBT types active electronicsemiconductor devices Q₁ can be connected, for example by means of anappropriate bias network schematically represented by the element R_(P),at the input terminal of the electronic adjustment stage 24 which isassumed to have a voltage potential which is positive (terminal T₁) orequal to zero (terminal T₂). The chosen type of connection is importantfor the choice of the active semiconductor devices Q₁ comprised withinthe electronic interruption circuit 41. For example, if the connectionoccurs at the terminal T₁, the electronic interruption circuit 41 caninclude MOSFET transistors of the N type or BJT transistors of the NPNtype, whereas if the connection occurs at the terminal T₂, theelectronic circuit 41 can include MOSFET transistors of the P type orBJT transistors of the PNP type.

[0043] Preferably, the comparator circuit block 44 comprises ahysteresis comparator 46, which is suitable to receive in input a signalV_(OUT1), indicative of the second unipolar voltage V_(OUT) and areference signal V_(REF). The reference voltage V_(REF) can be used toadjust the amplitude of the variation range of the voltage V_(OUT).

[0044] Advantageously, the enabling circuit block 45 comprises one ormore active electronic semiconductor devices Q₂ (for example of thepreviously described type), which are advantageously connected at theinput terminal T₁ or T₂.

[0045] According to the embodiment shown in FIG. 3, the chargeaccumulation circuit 23 comprises one or more capacitive elements 51,which are advantageously connected between the output terminals T₃ andT₄ of the adjustment stage 24.

[0046] Preferably, the second electronic means 26 comprise a network ofresistive elements 53 (elements R_(F1) and R_(F2)), which is suitable togenerate a feedback signal V_(F), indicative of the value of the secondcurrent I_(OUT). Advantageously, the second electronic means 26 alsocomprise one or more active semiconductor devices Q₃ (for example of theabove described type) which are suitable to generate, according to thefeedback signal V_(F), a control signal V_(COM) for the first electronicmeans 27. In particular, the active semiconductor devices 55 generatethe control signal V_(COM) (which can be an enable/disable signal) forthe electronic interruption circuit 41.

[0047] Preferably, the third electronic means 28 comprise a network ofcapacitive and/or resistive elements (elements R_(F3) and C_(F3)), whichis connected between one of the output terminals (T₃ or T₄) and thefirst electronic means 27.

[0048] The waveforms of some voltages and currents inside the adjustmentstage 24 are now illustrated schematically with reference to FIG. 4 inorder to make easier to understand the operation of the preferredembodiment illustrated in FIG. 3.

[0049] With reference also to FIG. 4, the waveform 60 schematicallyplots the voltage related to the node “A” of the adjustment stage 24.The peaks 61, related to the waveform 60, represent the enable/disablesignals V_(AB) sent by the electronic enabling circuit 45. Inparticular, the rising/falling edges (F₁ and F₂) of each peak 61respectively represent an enable/disable signal for the electronicinterruption circuit 41.

[0050] The waveform 62 instead plots the second current I_(OUT). It isclearly noticeable that at each peak 61 of the waveform 60 there is acurrent pulse 63 which is used to charge the charge accumulation circuit23. The slope of the rising/falling edges F₃ and F₄ related to eachcurrent pulse 63 is adjusted by the third electronic means 28 by sendingthe feedback signal V_(FREQ) to the first electronic means 27.

[0051] Considering the waveform 65, which plots the voltage V_(OUT), itcan be noted that the second current I_(OUT) charges the chargeaccumulation circuit 23.

[0052] As shown, after an initial transient 66, the voltage V_(OUT) canremain substantially constant by virtue of the action of the pulsedsecond current I_(OUT), which keeps charged, by virtue of successivepulses 63, the charge accumulation circuit 23. When the voltage V_(OUT)drops below a threshold value V_(S1), a rising edge F₁ of the waveform60 intervenes, causing the onset of the rising edge F₃ of the secondcurrent I_(OUT), which reaches a value corresponding to the value of thefirst current I_(IN). This causes a ramp-like increase R₁ of the voltageV_(OUT). As soon as the voltage V_(OUT) exceeds a threshold valueV_(S2), a rising edge F₁ of the waveform 60 intervenes and causes theonset of the rising edge F₃ of the second current I_(OUT), which returnsto zero. In this manner, the voltage V_(OUT) decreases, according to anexponential behavior R₂, which corresponds to the natural dischargetransient of the charge accumulation circuit 23.

[0053] The voltage V_(OUT) therefore has a ripple 67 whose maximum valuecan be adjusted by acting on the reference voltage V_(REF) of thehysteresis comparator 46.

[0054] In practice it has been found that the power supply device 20,according to the present invention, achieves the intended aim andobjects.

[0055] In particular, the power supply device 20 allows to supply anelectric power level, which is sufficient to supply electromagneticrelease devices, including release devices having relatively high powerconsumption, while limiting power dissipation. An adjustment of thefirst current I_(IN), for example according to a switching-type mode,allows to limit power dissipation only to the transients whichcorrespond to a rising/falling edge F₃ and F₄ of each pulse 63 of thesecond current I_(OUT). Moreover, by virtue of the adjustment of thefirst current I_(IN), the steady-state condition of the voltage V_(OUT)is possible after a relatively short transient period. Moreover, it hasbeen found that the power supply device 20 can be realized in arelatively compact size. Furthermore, it has been found to be easy tomanufacture, allowing achieving a considerable reduction inmanufacturing costs, installation costs and operating costs. Owing toits flexibility and operating characteristics, the power supply device20 has proved itself useful for very wide input voltage ranges.

[0056] The power supply device, according to the present invention, thusconceived is susceptible of numerous modifications and variations, allof which are within the scope of the inventive concept. All the detailsmay furthermore be replaced with other technically equivalent elements.In practice, the materials used, so long as they are compatible with thespecific use, as well as the dimensions, may be any according to therequirements and the state of the art.

1. A power supply device for low-voltage electronic residual currentcircuit breakers, comprising: an electronic rectifier stage, suitable toreceive in input a mains voltage and to generate a first unipolarvoltage, the value of said first unipolar voltage depending on the valueof said mains voltage; and an electronic adjustment stage, which issuitable to receive in input, from said electronic rectifier stage, saidfirst unipolar voltage and a first current and which is suitable togenerate in output a second unipolar voltage, which has an adjustablevalue; characterized in that said electronic adjustment stage comprisesfirst electronic means, suitable to perform an active adjustment of saidfirst current, so as to keep said second unipolar voltage at apredefined adjustable value.
 2. The power supply device, according toclaim 1, characterized in that said first electronic means perform anactive adjustment of said first current, in accordance to an adjustmentmode of the non-linear type.
 3. The power supply device, according toclaim 2, characterized in that said first electronic means perform anactive adjustment of said first current, in accordance to an adjustmentmode of the switching type.
 4. The power supply device, according to oneor more of the previous claims, characterized in that said firstelectronic means perform an active adjustment of said first current, soas to generate in output a second current, which has an adjustableaverage value.
 5. The power supply device, according to claim 4,characterized in that said second current is of the pulsed type, withadjustable pulse width and repetition period.
 6. The power supplydevice, according to one or more of the previous claims, characterizedin that said electronic adjustment stage comprises a charge accumulationcircuit, which is electrically connected to said first electronic means,said charge accumulation circuit receiving in input said second currentand generating said second unipolar voltage, the value of said secondunipolar voltage depending on the average value of said second current.7. The power supply device, according to one or more of the previousclaims, characterized in that said first electronic means comprise: anelectronic interruption circuit, which is suitable to enable/interrupt,following the reception of an enable/disable signal, said first current;and a comparator circuit block, which is suitable to generate a controlsignal when said second unipolar voltage assumes values above or below apreset range; and an enabling circuit block, which is suitable togenerate, following a control signal from said comparator circuit block,an enable/disable signal for said electronic interruption circuit. 8.The power supply device, according to previous claims, characterized inthat said second current of the pulsed type, whose pulse amplitude isequal to the amplitude of said first current and whose pulse durationcan be adjusted by said electronic control circuit.
 9. The power supplydevice, according to one or more of the previous claims, characterizedin that said electronic adjustment stage comprises second electronicmeans, which are electrically connected to said first electronic meansand are suitable to generate control signals for said first electronicmeans in order to limit to a predefined maximum threshold the amplitudeof the pulses of said second current.
 10. A power supply device,according to one or more of the previous claims, characterized in thatsaid electronic adjustment stage comprises third electronic means whichare electrically connected to said first electronic means and aresuitable to increase the stability of said electronic adjustment stage.11. The power supply device, according to claim 10, characterized inthat said third electronic means are capable to adjust the slope of therising/falling edges of the pulses of said second current.
 12. Alow-voltage electronic residual current circuit breaker, characterizedin that it comprises a power supply device, according to one or more ofclaims 1 to 11.